An Overview of Current and Future Vehicular Communication Technologies

The present paper provides a technical overview about the most relevant vehicular communication technologies including IEEE 802.11p, IEEE 802.11bd, LTEV2X and NRV2X. IEEE 802.11p is the most matured one Wi-Fi based technology, and its successor, the IEEE 802.11bd is expected to be released in 2021. As CV2X (Cellular Vehicle to Everything) technologies, LTEV2X (Long Term Evolution V2X) and NRV2X (New Radio V2X) are discussed in this paper. The former one is already available, while the latter one’s final specification will be finalized in 2020 by the 3GPP (Third Generation Partnership Project). These four technologies also motivate the already started transformation of vehicle industry by enabling basic safety features and more efficient traffic management, as well as cooperative maneuver execution towards high-level automated driving. The comparison of these technologies is essential to clarify their benefits completely. These technologies are considered as competitors, however, it is expected that they will coexist in the same geographical region. Thus, they will share on the same unlicensed frequency bands in 5.9 GHz domain. Therefore, different coexistence scenarios are also discussed in the paper to see how their advantages could be utilized

Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Open Platforms for Connected Vehicles

L'abstract è presente nell'allegato / the abstract is in the attachmen

Vehicular networks : IEEE 802.11p analysis and integration into an heterogeneous WMN

Tese de Mestrado Integrado. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201

Comunicações sem fios confiáveis para aplicações veiculares

Doutoramento em Engenharia ElectrotécnicaIn the last decades the number of vehicles travelling in European road has raised significantly. Unfortunately, this brought a very high number of road accidents and consequently various injuries and fatalities. Even after the introduction of passive safety systems, such as seat belts, airbags, and some active safety systems, such as electronic brake system (ABS) and electronic stabilization (ESP), the number of accidents is still too high. Approximately eight per cent of the fatal accidents occur in motorways, in the Portuguese case, the number of fatalities has remained constant in the first decade of the 21st century. The evolution of wireless communications, along with the north-American and European policies that reserve spectrum near the 5,9GHz band for safety applications in the vehicular environment, has lead to the development of several standards. Many of these applications are based on the possibility of using a wireless communication system to warn drivers and passengers of events occurring on the road that can put at risk their own safety. Some examples of safety applications are the hard-brake warning, the wrong-way warning and the accident warning. This work aims to contribute in defining a communication protocol that guarantees the timely dissemination of safety critical events, occurring in scenarios with a high number of vehicles or in the neighbourhood of so called motorway “blackspots”, to all vehicles in the zone of interest. To ensure information integrity and user trust, the proposed system is based on the motorway infrastructure, which will validate all events reported by the vehicles with the usage of several means, such as video surveillance or other sensors. The usage of motorway infrastructure that has full motorway coverage using fixed stations also known as road side units, allows to have a global vision of the interest zone, avoiding the problems associated to networks that depend solely on vehicle to vehicle communication, generally total ad-hoc networks. By using the infrastructure, it is possible to control medium access, avoiding possible badly intended intrusions and also avoiding the phenomenon known as alarm showers or broadcast storm that occur when all vehicles want to simultaneously access the medium to warn others of a safety event. The thesis presented in this document is that it is possible to guarantee in time information about safety events, using an architecture where the road side units are coordinated among themselves, and communicate with on board units (in vehicles) that dynamically register and deregister from the system. An exhaustive and systematic state of the art of safety applications and related research projects is done, followed by a study on the available wireless communications standards that are able to support them. The set of standards IEEE802.11p and ETSI-G5 was created for this purpose and is found to be the more adequate, but care is taken to define a scenario where WAVE enabled and non-enabled vehicles can coexist. The WAVE medium access control protocol suffers from collision problems that do not guarantee a bounded delay, therefore a new protocol (V-FTT) is proposed, based on the adaptation of the Flexible Time Triggered protocol to the vehicular field. A theoretical analysis of the V-FTT applied to WAVE and ETSI-G5 is done, including quantifying a real scenario based on the A5 motorway from Lisbon to Cascais, one of the busiest Portuguese motorways. We conclude the V-FTT protocol is feasible and guarantees a bounded delay.Nas últimas décadas tem-se assistido a um aumento do número de veículos a circular nas vias rodoviárias europeias, trazendo consigo um elevado número de acidentes e como consequência muitos feridos e vítimas mortais. Apesar da introdução de sistemas de segurança passivos, tais como cintos de segurança, airbags e de alguns sistemas de segurança activos, tais como o sistema electrónico de travagem (ABS) e o sistema electrónico de estabilidade (ESP), o número de acidentes continua a ser demasiado elevado. Aproximadamente oito por cento dos acidentes fatais na Europa ocorrem em auto-estradas, no caso Português, o número de vítimas mortais tem-se mantido constante ao longo da primeira década do século XXI. A evolução das comunicações sem fios, acompanhada de políticas europeias e norte-americanas no sentido de reservar frequências próximas dos 5,9GHz para aplicações de segurança no ambiente veicular, levou à especificação de várias normas. A maior parte destas aplicações baseiam-se na possibilidade de usar um sistema confiável de comunicação sem fios para alertar os condutores e passageiros de veículos para eventos ocorridos nas estradas que possam colocar em risco a sua segurança. Exemplos de aplicações de segurança crítica são o aviso de travagem brusca, o aviso de veículo em contra mão e o aviso de acidente na estrada. Este trabalho contribui para a definição de protocolos de comunicação capazes de garantir que a informação sobre eventos relacionados com situações de segurança crítica, que ocorram em cenários com um elevado número de veículos em zonas urbanas ou na vizinhança dos chamados “pontos negros” das auto-estradas, é disseminada com pontualidade por todos os veículos localizados na zona de interesse Por uma questão da integridade das comunicações e confiança dos condutores, o sistema proposto baseia-se na infra-estrutura do concessionário da auto-estrada, que validará os eventos reportados pelos veículos usando vários meios à sua disposição, como por exemplo sistemas de videovigilância e outros sensores. O uso de uma infra-estrutura de comunicações, que dispõe de cobertura integral a partir de estações fixas, permite uma visão global da zona coberta, evitando os problemas associados a redes baseadas apenas na comunicação entre veículos, que são em geral totalmente ad-hoc. O uso da infra-estrutura permite, entre outras vantagens, controlar o acesso ao meio, evitando simultaneamente intrusões de estranhos ao sistema e o fenómeno conhecido como “chuva de alarmes” desencadeado quando todos os veículos querem aceder simultaneamente ao meio para avisar os restantes da existência dum evento de segurança crítica. A tese apresentada neste documento defende que é possível garantir informação atempada sobre eventos que põem em risco a segurança dos veículos a partir de uma arquitectura de interligação entre as estações de comunicações fixas, coordenadas entre si, e unidades móveis (veículos) que se registam e se desligam dinamicamente do sistema. Nesta tese faz-se um levantamento exaustivo e sistemático das aplicações de segurança abordando projectos de investigação relacionados, estudam-se as tecnologias de comunicação sem fios disponíveis e a sua possibilidade de suportar aplicações de segurança rodoviária. Desta análise, conclui-se que a norma norte americana WAVE/IEEE802.11p e a europeia ETSI-G5, criadas especificamente para o efeito são as que mais se adequam à finalidade desejada. Considera-se que o cenário de utilização é evolutivo, podendo coexistirem veículos que não dispõem de sistemas de comunicação com outros que suportam a norma WAVE. Dado que o protocolo de acesso ao meio proposto pela norma WAVE não garante um acesso determinístico ao meio partilhado, propõe-se um novo protocolo, o Vehicular Flexible Time-Triggered protocol (VFTT). Faz-se a análise teórica da viabilidade do protocolo proposto para a norma WAVE e respectiva norma europeia (ETSI-G5). Quantifica-se o protocolo VFTT para um cenário real: a auto-estrada A5 Lisboa-Cascais, uma das autoestradas portuguesas mais movimentadas. Conclui-se que o protocolo é viável e garante um atraso restringido temporalmente

Design and analysis of LTE and wi-fi schemes for communications of massive machine devices

Existing communication technologies are designed with speciÿc use cases in mind, however, ex-tending these use cases usually throw up interesting challenges. For example, extending the use of existing cellular networks to emerging applications such as Internet of Things (IoT) devices throws up the challenge of handling massive number of devices. In this thesis, we are motivated to investigate existing schemes used in LTE and Wi-Fi for supporting massive machine devices and improve on observed performance gaps by designing new ones that outperform the former. This thesis investigates the existing random access protocol in LTE and proposes three schemes to combat massive device access challenge. The ÿrst is a root index reuse and allocation scheme which uses link budget calculations in extracting a safe distance for preamble reuse under vari-able cell size and also proposes an index allocation algorithm. Secondly, a dynamic subframe optimization scheme that combats the challenge from an optimisation solution perspective. Thirdly, the use of small cells for random access. Simulation and numerical analysis shows performance improvements against existing schemes in terms of throughput, access delay and probability of collision. In some cases, over 20% increase in performance was observed. The proposed schemes provide quicker and more guaranteed opportunities for machine devices to communicate. Also, in Wi-Fi networks, adaptation of the transmission rates to the dynamic channel condi-tions is a major challenge. Two algorithms were proposed to combat this. The ÿrst makes use of contextual information to determine the network state and respond appropriately whilst the second samples candidate transmission modes and uses the e˛ective throughput to make a deci-sion. The proposed algorithms were compared to several existing rate adaptation algorithms by simulations and under various system and channel conÿgurations. They show signiÿcant per-formance improvements, in terms of throughput, thus, conÿrming their suitability for dynamic channel conditions

Millimetre wave frequency band as a candidate spectrum for 5G network architecture : a survey

In order to meet the huge growth in global mobile data traffic in 2020 and beyond, the development of the 5th Generation (5G) system is required as the current 4G system is expected to fall short of the provision needed for such growth. 5G is anticipated to use a higher carrier frequency in the millimetre wave (mm-wave) band, within the 20 to 90 GHz, due to the availability of a vast amount of unexploited bandwidth. It is a revolutionary step to use these bands because of their different propagation characteristics, severe atmospheric attenuation, and hardware constraints. In this paper, we carry out a survey of 5G research contributions and proposed design architectures based on mm-wave communications. We present and discuss the use of mm-wave as indoor and outdoor mobile access, as a wireless backhaul solution, and as a key enabler for higher order sectorisation. Wireless standards such as IEE802.11ad, which are operating in mm-wave band have been presented. These standards have been designed for short range, ultra high data throughput systems in the 60 GHz band. Furthermore, this survey provides new insights regarding relevant and open issues in adopting mm-wave for 5G networks. This includes increased handoff rate and interference in Ultra-Dense Network (UDN), waveform consideration with higher spectral efficiency, and supporting spatial multiplexing in mm-wave line of sight. This survey also introduces a distributed base station architecture in mm-wave as an approach to address increased handoff rate in UDN, and to provide an alternative way for network densification in a time and cost effective manner

Physical and Link Layer Implications in Vehicle Ad Hoc Networks

Vehicle Ad hoc Networks (V ANET) have been proposed to provide safety on the road and deliver road traffic information and route guidance to drivers along with commercial applications. However the challenges facing V ANET are numerous. Nodes move at high speeds, road side units and basestations are scarce, the topology is constrained by the road geometry and changes rapidly, and the number of nodes peaks suddenly in traffic jams. In this thesis we investigate the physical and link layers of V ANET and propose methods to achieve high data rates and high throughput. For the physical layer, we examine the use of Vertical BLAST (VB LAST) systems as they provide higher capacities than single antenna systems in rich fading environments. To study the applicability of VB LAST to VANET, a channel model was developed and verified using measurement data available in the literature. For no to medium line of sight, VBLAST systems provide high data rates. However the performance drops as the line of sight strength increases due to the correlation between the antennas. Moreover, the performance of VBLAST with training based channel estimation drops as the speed increases since the channel response changes rapidly. To update the channel state information matrix at the receiver, a channel tracking algorithm for flat fading channels was developed. The algorithm updates the channel matrix thus reducing the mean square error of the estimation and improving the bit error rate (BER). The analysis of VBLAST-OFDM systems showed they experience an error floor due to inter-carrier interference (lCI) which increases with speed, number of antennas transmitting and number of subcarriers used. The update algorithm was extended to VBLAST -OFDM systems and it showed improvements in BER performance but still experienced an error floor. An algorithm to equalise the ICI contribution of adjacent subcarriers was then developed and evaluated. The ICI equalisation algorithm reduces the error floor in BER as more subcarriers are equalised at the expense of more hardware complexity. The connectivity of V ANET was investigated and it was found that for single lane roads, car densities of 7 cars per communication range are sufficient to achieve high connectivity within the city whereas 12 cars per communication range are required for highways. Multilane roads require higher densities since cars tend to cluster in groups. Junctions and turns have lower connectivity than straight roads due to disconnections at the turns. Although higher densities improve the connectivity and, hence, the performance of the network layer, it leads to poor performance at the link layer. The IEEE 802.11 p MAC layer standard under development for V ANET uses a variant of Carrier Sense Multiple Access (CSMA). 802.11 protocols were analysed mathematically and via simulations and the results prove the saturation throughput of the basic access method drops as the number of nodes increases thus yielding very low throughput in congested areas. RTS/CTS access provides higher throughput but it applies only to unicast transmissions. To overcome the limitations of 802.11 protocols, we designed a protocol known as SOFT MAC which combines Space, Orthogonal Frequency and Time multiple access techniques. In SOFT MAC the road is divided into cells and each cell is allocated a unique group of subcarriers. Within a cell, nodes share the available subcarriers using a combination of TDMA and CSMA. The throughput analysis of SOFT MAC showed it has superior throughput compared to the basic access and similar to the RTS/CTS access of 802.11

TOWARD ENHANCED WIRELESS COEXISTENCE IN THE 2.4GHZ ISM BAND VIA TEMPORAL CHARACTERIZATION AND EMPIRICAL MODELING OF 802.11B/G/N NETWORKS A DISSERTATION

This dissertation presents an extensive experimental characterization and empirical modelling of 802.11 temporal behavior. A detailed characterization of 802.11b/g/n homogeneous and heterogeneous network traffic patterns is featured, including idle time distribution and channel utilization. Duty cycle serves as a measure for spectrum busyness. Higher duty cycle levels directly impact transceivers using the spectrum, which either refrain from transmission or suffer from increased errors. Duty cycle results are provided for 802.11b, g and n Wi-Fi technologies at various throughput levels. Lower values are observed for 802.11b and g networks. Spectrum occupancy measurements are essential for wireless networks planning and deployment. Detailed characterization of 802.11g/n homogeneous and heterogeneous network traffic patterns, including activity and idle time distribution are presented. Distributions were obtained from time domain measurements and represent time fragment distributions for active and inactive periods during a specific test. This information can assist other wireless technologies in using the crowded ISM band more efficiently and achieve enhanced wireless coexistence. Empirical models of 802.11 networks in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band are also presented. This information can assist other wireless technologies aiming to utilize the crowded ISM band more efficiently and achieve enhanced wireless coexistence. In this work models are derived for both homogeneous and heterogeneous 802.11 network idle time distribution. Additionally, two applications of 802.11 networks temporal characterization are presented. The first application investigates a novel method for identifying wireless technologies through the use of simple energy detection techniques to measure the channel temporal characteristics including activity and idle time probability distributions. In this work, a wireless technology identification algorithm was assessed experimentally. Temporal traffic pattern for 802.11b/g/n homogeneous and heterogeneous networks were measured and used as algorithm input. Identification accuracies of up to 96.83% and 85.9% are achieved for homogeneous and heterogeneous networks, respectively. The second application provides a case study using 802.15.4 ZigBee transmitter packet size on-line adjustments is also presented. Packet size is adaptively modified based on channel idle time distribution obtained using simple channel power measurements. Results demonstrate improved ZigBee performance and significant enhancement in throughput as a result of using adaptive packet size transmissions

Achieving Low latency and High Packet Reception Ratio in Media Access Control Layer in VANET

Vehicular ad hoc networks (VANETs) or inter-vehiclecommunication (IVC) makes possible the development of a number ofinnovative and powerful transportation system applications. VANETtechnology proves an important extension of both cellular andwireless local area networks (WLANs) currently used in thetransportation industry. It is widely recognized that thetransportation industry serves as an ideal platform for a largenumber of existing and future wireless applications, many of whichhave yet to be developed for commercial use.Safety messaging is one of the most critical uses for VANET,supporting a number of potential safety applications, e.g. emergencyelectronic brake lights, lane change and pre-crash warning, amongothers. Many applications require extremely low latency (less than100ms) and highly reliable (over 99\% packet delivery ratio)communication services. In order to satisfy these criticalrequirements, an efficient media access control (MAC) layer isnecessary. At the time of this writing, a de facto standard of VANETMAC is being developed.Extensive VANET MAC research with regard to safety applications hasyet to be done. The proposed base for the VANET future standard usesan 802.11a media access layer whose performance-although studied-isknown to contain deficiencies and was accomplished outside theVANET context. These factors motivated the author to initiate thestudy of VANET and MAC.In this work, MAC for VANET MAC is extensively researched, and ahistory of MAC is initially reviewed. The special and criticalrequirements of VANET MAC are presented and four major categorieswere investigated and analyzed. Because the under-development of802.11p is based on the IEEE 802.11a, special consideration is givenwith regard to the performance of 802.11a MAC and associatedrequirements. Extensive research enhancements centering on safetyapplications of the 802.11 MAC are conducted. The author's researchgenerated a platform in which VANET performance can bequantitatively evaluated, analyzed, and verified. The quantitativebehavior of the current protocols/algorithms, which include delayand packet delivery ratio, are presented on this platform.Furthermore, the future protocol and algorithm proposals can beadded into this platform so that a faster research cycle can beachieved. Through theoretical analysis and simulation, thisinvestigation shows that current proposed VANET MAC and 802.11a MACenhancements have yet met the critical requirements of VANET. Thefuture work may focus on how to use this theoretical model andsimulation tool to assist MAC layer protocol design. Meanwhile, whennew algorithms are proposed or accepted by the standard, this modeland tool can serve as a fast and convenient platform, where the newalgorithm can be easily added for the sake of evaluation andverification. The feasibility of relaxing some assumptions includedtherein, such as the hidden node problem in a two dimensional space,may also be studied to make the platform closer to a real system